(1) Field of the Invention
This invention relates to a field emission type display device including field emission elements acting as electron sources inside a thin container and a getter room formed adjacent to the thin container.
(2) Description of the Related Art
A field emission type display device (panel) having field emission elements as electron sources (hereinafter sometimes referred to as FED) has been known as a fluorescent display tube of which the thin container contains field emission elements acting as electron sources.
FIGS. 9(a) and 9(b) partially illustrate the configuration of a container for that type of FED. In the field emission type display device shown in FIG. 9(b), the anode substrate 54 has the display portion 53 formed of the fluorescent material layer 51 and the metal-backed layer 52. The cathode substrate 56 has the inner surface on which the field emission elements 55 are formed so as to confront the display portion 52 formed on the anode substrate 54. The container 27 is formed by hermetically sealing the anode substrate 54 and the cathode substrate 56 at the peripheral portions thereof, with the substrates spaced from each other a predetermined distance.
In the FED, the anode substrate 54 and the cathode substrate 56 are formed of a thin glass plate, respectively. The gap between the substrates 54 and 56 is very narrow.
In order to function the FED as a display device, the inside of the container must be maintained a high vacuum degree such that the field emission element 55 can effectively emit electrons.
However, since the container 57 of the FED is very thin, the getter member that adsorbs gas produced in the container 57 cannot be placed inside the container 57. A getter room, as shown in FIG. 9(a), is additionally formed by assembling a box-like cover member 58 on the outside of the container 57. A getter film is formed by evaporating the getter in the getter room.
In the above-mentioned FED, since electrons emitted from the field emission element 55 onto the fluorescent material layer 51 radiate light, a metal-backed layer 52 of a conductive material such as aluminum is deposited so as to cover the whole surface of each of dot-like fluorescent material layers 51. Moreover, as shown in FIG. 9(a), a part of the metal-backed layer 52 is derived to the end portion of the anode substrate 54 to form the anode electrode 59. An additional electrode is formed to the anode terminal 59 to connect electrically to the drive circuit.
In the FED of the type which has an anode electrode to which a high anode voltage of, for example, 2 to 10 kV is applied, it is needed to secure safety, easy-to-connection, and mass-productivity when the conductor acting as an anode derived from the display portion 53 is electrically connected to an external drive circuit.
In the above-mentioned conventional FED, the anode substrate 54 and the cathode substrate 56, as shown in FIG. 9(a), must be arranged so as to be shifted somewhat in plane to apply an anode voltage on the metal back layer 52 coated over the fluorescent material layer 51. Moreover, the anode electrode 59 must be placed so as to drive a part of the metal-backed layer 52 toward the outside of the container 57. Additional electrode must be arranged to connect the anode terminal 59 to the drive circuit.
However, since the metal-backed layer 52 coated on the fluorescent material layer 51 is formed in close contact with the surface of the anode substrate 54, together with the anode terminal 59, it is difficult to connect easily the electrode to the anode thermal 59. Moreover, the high voltage applied may cause a decrease in safety because of the difficulty in connection.
Usually, the anode substrate 54 and the cathode substrate 56 are hermetically fixed with a sealing agent filled in the spaces between the peripheral portions of them. This sealing agent has a dielectric strength lower than that of the substrates 54 and 56. The anode electrode 59 formed as a part of the metal-backed layer 52 or formed differently from the metal-backed layer 52 and electrically connected to each other is derived to the end portion of the anode substrate 54 in contact with the sealing agent.
However, when a high anode voltage is applied to the metal-backed layer via the additionally-formed electrode, the sealing agent may result in its dielectric breakdown because of the short distance between the substrates 54 and 56. The dielectric breakdown of the sealing agent may cause undesired current rushing into other components such as the cathode substrate 56 confronting the anode substrate 54 and field emission elements formed on the cathode substrate 56. As a result, the problem that the FED is not normally glowed arises.